Magnetic disk device and method for measuring counter electromotive voltage of spindle motor

Abstract

According to an embodiment, a magnetic disk device includes a magnetic disk, a spindle motor that rotates the magnetic disk, a motor driver, and a controller. The motor driver supplies a motor current to the spindle motor and measures a counter electromotive voltage of the spindle motor every time the spindle motor makes one rotation. After the rotation of the magnetic disk starts, the controller adjusts a motor position where the counter electromotive voltage is measured to a set first position.

What is claimed is: 
     
       1. A magnetic disk device comprising:
 a magnetic disk; 
 a spindle motor that rotates the magnetic disk; 
 a motor driver that supplies a motor current to the spindle motor and starts measuring a counter electromotive voltage of the spindle motor every time the spindle motor makes one rotation at a first position among a plurality of second positions, each of the plurality of second positions being a motor position where a value of the motor current crosses zero; and 
 a controller that changes, after the magnetic disk starts rotating, a motor position where the counter electromotive voltage is measured every time the spindle motor makes one rotation from the first position to a set third position among the plurality of second positions. 
 
     
     
       2. The magnetic disk device according to  claim 1 , wherein
 the motor driver is capable of operating in any operation mode of a first mode in which the counter electromotive voltage is measured only at one of the plurality of second positions and a second mode in which the counter electromotive voltage is measured at all of the plurality of second positions, and 
 after the magnetic disk starts rotating, the motor driver transitions from the second mode to the first mode and measures the counter electromotive voltage only at the third position. 
 
     
     
       3. The magnetic disk device according to  claim 2 , further comprising
 a magnetic head, 
 wherein servo information is recorded in the magnetic disk, 
 the controller reads the servo information by the magnetic head, and 
 the motor driver transitions from the second mode to the first mode at a timing based on the servo information read by the magnetic head. 
 
     
     
       4. The magnetic disk device according to  claim 1 , wherein
 the controller executes control to learn repeatable run-out (RRO) and write a learned value of the RRO to the magnetic disk, 
 the motor driver measures the counter electromotive voltage at a fourth position during the learning of the RRO, and 
 the controller sets the fourth position as the third position. 
 
     
     
       5. The magnetic disk device according to  claim 4 , further comprising
 a magnetic head, 
 wherein servo information is recorded in the magnetic disk, and 
 the controller stores a positional relationship between a reference position based on the servo information and the fourth position. 
 
     
     
       6. The magnetic disk device according to  claim 5 , wherein
 the motor driver controls a rotational speed of the spindle motor based on a measured value of the counter electromotive voltage. 
 
     
     
       7. The magnetic disk device according to  claim 1 , wherein
 the first position is, among the plurality of second positions, a second position depending on a position of the spindle motor at a time of start-up of the magnetic disk device. 
 
     
     
       8. A method for controlling a magnetic disk device, which includes: a magnetic disk; a spindle motor that rotates the magnetic disk; and a motor driver that supplies a motor current to the spindle motor, the method comprising
 starting measuring a counter electromotive voltage of the spindle motor every time the spindle motor makes one rotation at a first position among a plurality of second positions, each of the plurality of second positions being a motor position where a value of the motor current crosses zero; and 
 changing, after the magnetic disk starts rotating, a motor position where the counter electromotive voltage is measured every time the spindle motor makes one rotation from the first position to a set third position. 
 
     
     
       9. The method according to  claim 8 , wherein
 the motor driver is capable of operating in any operation mode of a first mode in which the counter electromotive voltage is measured only at one of the plurality of second positions and a second mode in which the counter electromotive voltage is measured at all of the plurality of second positions, and 
 after the magnetic disk starts rotating, the motor driver transitions from the second mode to the first mode and measures the counter electromotive voltage only at the third position. 
 
     
     
       10. The method according to  claim 9 , further comprising
 reading servo information by a magnetic head, 
 wherein the magnetic disk device further includes the magnetic head, 
 the servo information is recorded in the magnetic disk, and 
 the motor driver transitions from the second mode to the first mode at a timing based on the servo information read by the magnetic head. 
 
     
     
       11. The method according to  claim 8 , further comprising:
 executing control to learn repeatable run-out (RRO) and write a learned value of the RRO to the magnetic disk; and 
 setting a fourth position as the third position, 
 wherein the motor driver measures the counter electromotive voltage at the fourth position during the learning of the RRO. 
 
     
     
       12. The method according to  claim 11 , further comprising
 storing a positional relationship between a reference position based on servo information and the fourth position, 
 wherein the magnetic disk device further includes a magnetic head, and 
 the servo information is recorded in the magnetic disk. 
 
     
     
       13. The method according to  claim 8 , wherein
 the first position is, among the plurality of second positions, a second position depending on a position of the spindle motor at a time of start-up of the magnetic disk device.